Conventional aircraft instruments used in aerial navigation present data, such as compass bearings and headings, distances, times, etc., in the form of gauges, and numerical readouts. A pilot or navigator must mentally interpret these readings with reference to an approach chart or the like in order to obtain a mental visualization of the location of his aircraft relative to reference points depicted on the chart. This mental process is time consuming and subject to error. An automatic pictorial presentation of the relationship of the aircraft to its ground position on the chart eases the task of the pilot and contributes to air safety.
Some modern fighter aircraft have CRT displays which shows the aircraft above a chart image produced in the CRT; however, the pilot has no way of knowing if the information on such displays is accurate, and if the display fails, the chart disappears leaving the pilot "blind." Further, such devices are prohibitively expensive.
When an aircraft is flying in clouds (blind) under Instrument Flight Rules there is a continuous need for a quick and reliable positional fix of an aircraft relative to ground elevations, airports, navigational aids, etc., shown on charts. Air traffic control procedures in the vicinity of airports often require a pilot to follow radio instructions from a distant air traffic controller situated on the ground. The controller monitors the location and movement of an aircraft by radar, plus signals from a transponder on the aircraft and vectors the aircraft. During such radar vectoring, a controller often requests numerous turns and changes of altitude of the aircraft to meet traffic conditions, weather conditions, ground elevations, etc.
A frequent result of such vectoring, during approach (or departure) control, is that the pilot loses a clear perception of the location of the aircraft relative to its ground position and becomes more or less dependent on the instructions from the controller. Such dependency is a source of discomfort among pilots because a controller's equipment can sometimes fail to fix the location of the aircraft accurately and controllers also make mistakes. Thus, pilots need an instrument for visually showing the location of the aircraft relative to the airport, terrain, and obstacles during a radar vectoring. With such an instrument, a pilot is able to detect possible errors in the controller's instructions and to take such action that the situation might require of a pilot-in-command to meet his legal responsibility of a safe flight. Such an instrument provides assurance to the pilot by providing a visual display of the position of the aircraft over the terrain relative to a chart information.
Problems arising from the form of data presentation now provided by conventional aircraft instruments are not confined to landings and take offs under instrument flight rules. Avoidance of hills, mountains, vertical structures or other obstacles prior to the approach control phase is often dependent on radar vectoring by an air traffic controller because of fog, clouds or darkness. Crashes into terrain or vertical obstacles occur with an alarming frequency while aircraft are being vectored, usually with fatal results. A convenient and reliable instrument for independent displaying the relationship of the aircraft to such obstacles for the pilot can forestall such crashes in most cases.
Pilots operating under visual flight rules [VFR] can also benefit from a device displaying their aircraft's location and direction in reference to charts. For example, pilots flying near, under, above or within Terminal Control Areas which have a complex pattern of layered zones for different types of aircraft also need accurate visual information as to their location within or about such zones. Safe navigation in such areas requires a continuous awareness of the location and direction of the aircraft relative to both the horizontal and vertical boundaries of such controlled zones.
The present invention is directed to providing the above advantages and overcoming more than one of the problems discussed above.